Digital images are commonly used in several applications such as, for example, in digital still cameras (DSC). A digital image includes a matrix of elements, commonly referred to as a bit map. Each element of the matrix, which represents an elemental area of the image (a pixel or pel), is formed by several digital values indicating corresponding components of the pixel. Digital images are typically subjected to a compression process to increase the number of digital images which can be stored simultaneously, such as onto a memory of the camera. Moreover, this allows transmission of digital images to be easier and less time consuming. A compression method commonly used in standard applications is the JPEG (Joint Photographic Experts Group) algorithm, described in CCITT T.81, 1992.
In a basic JPEG algorithm, 8×8 pixel blocks are extracted from the digital image. Discrete Cosine Transform (DCT) coefficients are then calculated for the components of each block. The DCT coefficients are rounded off using corresponding quantization tables. The quantized DCT coefficients may be entropy coded utilizing probability tables to obtain a compressed digital image. Entropy coding may be performed by using Arithmetic encoding or by using Huffman coding. The original digital image may be extracted later from the compressed version of the image by a decompression process.